Minor rephrasing of errors / logs
Minor rephrasing of errors / logs

- Use "failed to", as it's used in many other locations,
  so more consistent
- Removed "Swarm successfully ...", as it should be clear
  from the rest of the message

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

docker/swarmkit,docker/swarmkit